In recent years, various methods have been studied to form an electric conductor by forming a pattern employing an ink comprising a dispersion having fine particles of a metal such as copper or silver dispersed in a liquid, followed by a heat treatment so that the metal fine particles are mutually sintered. Such methods may, for example, be a method of carrying out formation, repair or the like of a circuit pattern such as printed wiring, interlaminar wiring in a semiconductor package, or connection of a printed wiring board with an electronic component, by means of an ink jet printing method (Patent Document 1), a method of joining metals which replaces conventional soldering (Patent Document 2), and a method of forming an electrically conductive metal film capable of replacing a plated film in the field of electronic materials (Patent Document 3). Further, recently it has been disclosed that a metallic material can constantly be obtained by using a dispersion containing fine copper hydride particles which are hardly oxidized and excellent in storage stability (Patent Document 4).
The above methods for forming conductive metal films employ known nature called surface melting of metal particles (Non-Patent Document 1). It is generally known that the surface melting of metal particles takes place due to abnormal lattice vibration of atoms at the surface of the particles, and that the smaller the particle diameter and the higher the proportion of surface atoms, the more the surface melting temperature decreases. For example, in a case of copper, it is known that bulk copper has a melting point of 1,083° C., whereas fine particles having diameters of about 10 nm undergo the surface melting at a temperature of about 150° C. Since the surface melting depends on the particle diameter of the metal particles, it takes place even in an association state so long as individual fine metal particles have a predetermined particle diameter, unless particles are completely bound.
However, the coating film formed by any one of the above methods had no adequate adhesive strength when the substrate was highly flat such as a glass substrate. Further, the coating film was formed by utilizing the surface melting phenomenon, and in a case where fine metal particles having a large particle diameter at a level of μm size were used, the adhesive strength of the fine metal particles to one another was weak, and it was not possible to obtain a film having adequate strength. Further, in a case where a conductive metallic material was formed for wiring by using fine silver particles, there was a specific problem that ion migration took place, and an improvement to overcome such a problem has been desired.    Patent Document 1: JP-A-2002-324966    Patent Document 2: JP-A-2002-126869    Patent Document 3: JP-A-2002-334618    Patent Document 4: WO2004/110925    Non-Patent Document 1: “J. Sol-Gel Science and Technology” the Netherlands, Kluwer Academic Publishers, 2001, vol. 22, pages 151 to 166